feat(lsp): deprecate vim.lsp.start_client #31341

Problem:
LSP module has multiple "start" interfaces.

Solution:
- Enhance vim.lsp.start
- Deprecate vim.lsp.start_client

test/functional/plugin/lsp/diagnostic_spec.lua

@@ -89,7 +89,7 @@ describe('vim.lsp.diagnostic', function()
         return extmarks
       end
 
-      client_id = assert(vim.lsp.start_client {
+      client_id = assert(vim.lsp.start({
         cmd_env = {
           NVIM_LUA_NOTRACK = '1',
         },
@@ -101,7 +101,7 @@ describe('vim.lsp.diagnostic', function()
           '--headless',
         },
         offset_encoding = 'utf-16',
-      })
+      }, { attach = false }))
     end)
 
     fake_uri = 'file:///fake/uri'

test/functional/plugin/lsp/semantic_tokens_spec.lua

@@ -456,7 +456,7 @@ describe('semantic token highlighting', function()
         vim.notify = function(...)
           table.insert(_G.notifications, 1, { ... })
         end
-        return vim.lsp.start_client({ name = 'dummy', cmd = _G.server.cmd })
+        return vim.lsp.start({ name = 'dummy', cmd = _G.server.cmd }, { attach = false })
       end)
       eq(false, exec_lua('return vim.lsp.buf_is_attached(0, ...)', client_id))
 

test/functional/plugin/lsp_spec.lua

@@ -95,7 +95,7 @@ describe('LSP', function()
       exec_lua(function()
         _G.lsp = require('vim.lsp')
         function _G.test__start_client()
-          return vim.lsp.start_client {
+          return vim.lsp.start({
             cmd_env = {
               NVIM_LOG_FILE = fake_lsp_logfile,
               NVIM_APPNAME = 'nvim_lsp_test',
@@ -112,7 +112,7 @@ describe('LSP', function()
                 name = 'test_folder',
               },
             },
-          }
+          }, { attach = false })
         end
         _G.TEST_CLIENT1 = _G.test__start_client()
       end)